I have been to eight of Trump's rallies in several states over the last two months, and I have seen protesters removed or jeered at each one, but I have not seen anything that could be described as a serious brawl.

In Trump's months of campaigning before growing and fired-up audiences, some of them so large they packed stadiums, no one has been seriously injured -- and that includes the police officer and two civilians who were briefly taken to a hospital after the canceled rally in Chicago on Friday. A punch, a reporter pushed to the ground: This is hardly the mayhem that sometimes accompanies politics in what Rubio calls "the Third World."

In younger and poorer democracies, there's more violence in parliaments than there has been at Trump rallies. In Greece, demonstrations against pension reform routinely feature Molotov cocktails and tear gas. In Ukraine last August, a hard-right activist threw a hand grenade at the police at a rally outside the parliament building, and shots were fired, resulting in the death of an officer and 100 serious injuries. In Russia, attending a rally that is not officially sanctioned carries the risk of beatings and detention. Hundreds invariably are.

We can hope that Trump tones things down while at the same time remembering that the U.S. has a long tradition of muscular politics characterized by flare-ups that go far beyond shouting matches and some pushing.

Consider the civil rights protests or those against the Vietnam War, not to mention the labor clashes of the 1920s and 1930s.

It's not just the U.S., either. "As comforting as it is for civilized people to think of barbarians as violent and of violence as barbarian, Western civilization and various forms of collective violence have always clung to each other," the sociologist Charles Tilly wrote in 1978.

But the relative calm in U.S. politics may just be cyclical. This season may be more contentious because Americans are getting impatient with politics as usual, whether from the left or from the right. Around the world and throughout history, similar impatience sometimes has found expression in violence.

Brawling at rallies is not necessarily the sign of a descent into barbarity. It may just be a manifestation of intensified anger and conviction, which often go hand in hand. Democracy can be messy, especially when a country is changing. I've seen in one post-Soviet country after another that the past doesn't give up without a fight. But all hope for change dies when people grow apathetic, stop fighting, then stop showing up.

This election may not be a showcase for the intelligence and statesmanship of the U.S. elite, but the passion and engagement it has infused into U.S. politics could have a silver lining.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.